What was found
UPON COMPLIANCE OF LYCOMING SB 518B, FOUND NUT MISSING. THE NUT WAS LOCATED INSIDE OIL COOLER WITH THE WRENCH FLATS OF THE NUT COMPLETELY ROUNDED OFF. OUT OF 14 ACFT, THIS SHOP HAS INSPECTED, HAVE HAD TO REPLACE 12 BYPASS VALVES. HIGHLY RECOMMEND THIS SB BECOME AN AD. THERE WAS BARELY ANY INDICATION ON THE CRIMPED PART OF THE NUT.